Obstetric Anesthesia

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At present, many pregnant women are choosing to receive analgesia to relieve the pain of childbirth through several methods. More than 50% of women in labor are reported to choose intrapartum epidural analgesia at many U.S. institutions. This probably reflects changing societal expectations and increasing participation in the birth process on the part of both anesthesiologists and certified registered nurse anesthetists.

Pain during the first stage of labor is attributable to uterine contractions and cervical dilation. Afferent impulses from the cervix and uterus are transmitted to the spinal cord via the tenth thoracic to first lumbar (T10-L1) segments. Pain is conducted along the paracervical and inferior hypogastric plexus. During the second stage, pain also occurs from distention and stretching of pelvic structures and the perineum. Second-stage pain is principally somatic in nature and is transmitted through the spinal second to fourth sacral (S2-S4) segments.

Therapeutic modalities to manage the pain of childbirth include systemic narcotics, local anesthesia, and psychological methods (Howell, 2000). Systemic narcotics used to manage pain during labor include meperidine (Demerol, 25 mg IM or IV) and nalbuphine (Nubain, 10 mg IV). Narcotics should be avoided at or near delivery because they can cause nausea, vomiting, decreased gastric motility, and respiratory depression and can interfere with the mother's ability to concentrate and cooperate. Fetal effects include respiratory and CNS depression and temperature instability. Naloxone (0.01 mg/kg) can be administered to depressed newborn as an IV bolus for counteracting the effect of narcotics.

A pudendal block provides analgesia to the vaginal introi-tus and perineum. Usually done in the second stage of labor, 5 mL of 1% lidocaine is injected into the pudendal canal, the location of the pudendal nerves and vessels. Care is taken to aspirate for blood before instilling the anesthetic solution. It takes approximately 10 minutes for anesthesia to establish. Infection at the injection site, intravascular injection, and maternal overdose are the major potential complications.

Neuraxial or epidural analgesia is popular among both physicians and patients (Vincent and Chestnut, 1998). The anesthesiologist's goal for epidural analgesia during the first stage of labor is to provide segmental sensory anesthesia of the T10 to L1 dermatomes. The dose of anesthetic necessary to achieve effective labor analgesia will depend on the intensity and location of the patient's pain. These in turn depend on the amount and rate of cervical dilation; the strength, frequency and duration of uterine contractions; and the position of the fetal head at the time epidural analgesia is placed. Typically, bupivacaine (Marcaine) or ropivacaine (Naropin), with or without a small dose of a lipid-soluble opioid such as fentanyl (Sublimaze) or sufentanil (Sufenta), establishes effective analgesia with minimal motor block. Maintenance of epidural analgesia may be achieved with intermittent bolus injections, continuous infusion, or patient-controlled dosing frequency.

Although epidural analgesia provides superior pain relief during labor, much controversy surrounds its drawbacks. These include the increased duration of labor, increased need for oxytocin augmentation, and increased rate of cesar-ean section for failure to progress. The most common complications, however, are maternal hypotension and headache from inadvertent puncture of the dura.

Contraindications to epidural analgesia include patient refusal, active maternal hemorrhage, maternal septicemia or untreated febrile illness, infection at or near needle insertion site, and maternal coagulopathy.

Psychological methods of pain relief include Lamaze, natural-childbirth methods, acupuncture, biofeedback, and

Figure 21-16 Crowning fetal head distending the perineal tissues. Broken lines depict the location of the incision for a midline (median) or mediolateral episiotomy.

Box 21-11 Categories of Perineal and Vaginal Lacerations

First degree: Confined to the superficial skin or mucosa; repair usually not required unless extensive or bleeding.

Second degree: Involves the mucosa and deeper tissues of the vagina and perineum.

Third degree: Involves the anal sphincter.

Fourth degree: Involves the rectal mucosa and usually transects the anal sphincter.

self-hypnosis. These techniques are useful in decreasing maternal anxiety and may reduce the amount of analgesia needed.

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Pregnancy And Childbirth

Pregnancy And Childbirth

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